But how could Terry seem so upbeat when the Celtics are being beaten down, on defense and with injuries and other issues that have kept their stars off the court?

Aren’t there concerns these struggles could stretch into the playoffs?

If any of those worries were floating around Terry’s mind, he didn’t voice them after the Celtics fell to Minnesota, 110-100, on Monday night. Instead, Terry, in his 14th season, dug through his NBA résumé for anecdotes to back up his claims of optimism.

“I’ve seen a lot,” the 35-year-old said. “I’ve been around so long, where I’ve won 67 games and been out in the first round — not fun. I’ve been all the way to the Finals and got a heartbroken; [I’ve] been there and won it. There’s nothing I haven’t seen.

“But the main thing is, being optimistic, sticking together. Right now, we stay together, we get healthy, we go into the playoffs feeling good about ourselves and it’s going to be a fun ride.”

The way the Celtics, who face Detroit Wednesday at TD Garden, are playing toward the end of the regular season would not be called “fun” by anyone — except, perhaps, opposing teams.

Kevin Garnett’s absence because of a sore left ankle has opened a gaping hole in the paint that teams have exploited nightly, piling up points around the rim.

Garnett has missed six games and is day to day with his injury. The Celtics brass is taking a cautious approach with Garnett in part because the team needs the 36-year-old to be healthy and fresh for a postseason run.

The team said last week Garnett could miss up to two weeks, and the Celtics will probably have to digest a few more losses as Garnett sits out. There’s just not much else they can do. But, Terry said the team can tighten up on its defensive mistakes and, most important, prepare their mind-set for the playoffs.

“Playoffs is the best time of the year, for everyone. And especially when it’s so, so close. That’s when you really have to lock in and focus up there,” Terry said, pointing to his head. “It’s going to be mental more than anything.”

Terry continued: “Whatever you have to do individually to do that, that’s what we have to do, because you’re going to have to be so locked in, whether it’s a defensive assignment, whether it’s offensively, knowing where you’re supposed to be. We can’t have any slippage.

“Again, with the roster we have, there’s no margin for error. We’ve got to be locked in. It’s more evident the more and more we play these games and you’ve got this guy sitting out, [that] guy [sitting out]. The same thing can happen in the playoffs. You don’t know who you’re going to have, but whoever we go out there with, we must execute on both ends of the floor.”

It might seem like it would be tough for these Celtics to focus on their last eight regular-season games with the playoffs so close, but Avery Bradley said that’s not the case.

“Because our vets on our team, they use these games as practice [for the playoffs],” he said. “Every game for us is serious. We want to win every single game, but we want to improve as a team every single game. Paul [Pierce] and those guys let us know before every single game. When we’re in the huddle, he lets us know that we need to keep taking steps forward to prepare for the playoffs.”

Bradley looks better

One silver lining from the Celtics loss Monday was Bradley, who emerged from a long offensive slump to score a team-high 19 points on 8-of-14 shooting.

In the 13 games entering Monday, Bradley had been averaging 7.2 points on 31 percent shooting from the floor.

“All you can do is continue to get shots up and stay confident,” Bradley said. “That’s what I did. My teammates, after every single game, I might be down and they’re there, lifting me up, telling me to keep going.”

Bradley had said that there wasn’t anything specifically wrong with his shot and that his slump was just a confidence issue. Celtics coach Doc Rivers said they’ve tried to help him in five straight games by having Bradley shoot on the team’s first play of the game. After, Rivers said he told Bradley that the arc on his shot had returned whereas before the guard’s shots were too flat.